Tunable filter for LTE bands

ABSTRACT

A tunable filter reduces the total number of filters used in TDD (Time-Division Duplex) communication circuitry. The communication circuitry may include a tunable filter and a first switch associated with the tunable filter. The tunable filter may include a tuning component and a filtering component. The tuning component may be located with the first switch on a first die. The filtering component may be located in a laminate underneath the first switch. Power amplifiers for amplifying transmission signals may be located on a second die, and the second die may be located on the laminate.

RELATED APPLICATIONS

This application claims priority to and is a divisional of U.S. patentapplication Ser. No. 15/943,817, filed on Apr. 3, 2018, now patented asa U.S. Pat. No. 10,237,050 on Mar. 19, 2019, which is a divisional ofU.S. patent application Ser. No. 14/230,620, filed on Mar. 31, 2014, nowU.S. Pat. No. 9,935,760, which claims the benefit of provisional patentapplication Ser. No. 61/812,454, filed Apr. 16, 2013, the disclosures ofwhich are hereby incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The field of the disclosure is filtering signals in LTE-TDD (Long TermEvolution Time-Division Duplex) bands. Specifically, communicationcircuitry includes a tunable filter to reduce the total number offilters used and includes a switch to facilitate TDD operation of thetunable filter. The tunable filter may include a tunable element that islocated on a same die as the switch.

BACKGROUND

A conventional communication circuit may use 9 SAW (Surface AcousticWave) filters. These SAW filters facilitate split band coverage to avoidinterference with a central ISM (Industrial Scientific and Medical, orWiFi) band.

Filters in a conventional communication circuit are unidirectional, andthus either filter transmission (TX) signals or filter reception (RX)signals (but never both).

FIG. 1 illustrates a conventional communication circuit with its majorcomponents. Specifically, FIG. 1 illustrates: communication circuitryCOMCKT including controller CKT14, transceiver CKT2, diversity filtersCKT4, diversity switches CK6, high band pad CKT8, high band filtersCKT10, high band switches CKT12, diversity antenna ANTDIV, and mainantenna ANTMAIN. Additionally, FIG. 2 illustrates details of transceiverCKT2, diversity filters CKT4, and diversity switches CKT6. FIG. 3illustrates details of high band pad CKT8, high band filters CKT10, andhigh band switches CKT12.

Controller CKT14 may control: transceiver CKT2 through control line CL2,diversity filters CKT4 through control line CL4, diversity switches CKT6through control line CL6, high band pad CKT8 through control line CL8,high band filters CKT10 through control line CL10, and ultrahigh bandswitches CKT12 through control line CL12. Controller CKT14 may include aprocessor and a non-transitory memory.

A control line such as CL2 may include (not shown) a voltage supply, aserial data line, parallel data lines, a clock signal, a ground, poweramplifier control signals, switch control signals, and may also includereturn signals such as signal power measurements.

FIGS. 2A and 2B illustrate a conventional transceiver, diversityfilters, and diversity switches from FIG. 1. Specifically, FIGS. 2A and2B illustrate exemplary details of transceiver CKT2, diversity filtersCKT4, and diversity switches CKT6 from FIG. 1.

Transceiver CKT2 includes many nodes. The node names indicate what bandsare transmitted or received by the specific node. Further, “TX”indicates that a main signal is being transmitted. “DRX” indicates thata diversity signal is being transmitted. “RX” indicates that a mainsignal is received. Thus, the top node is named “B7 TX,” indicating thata main signal (S2) in band 7 is transmitted. Further, bands such as band40 may be referred to as “band B40” for emphasis that the number “40”refers to a band. Additionally, a filter may be referred to as filtering“band B40 RX” to emphasize that the signal being filtered is a receivedsignal.

From top to bottom, the nodes may be grouped as follows: transmittingmain signals; receiving filtered diversity high band signals from switchSW2 of diversity switches CKT6; receiving filtered diversity low bandsignals from switch SW4 of diversity switches CKT6; and receiving othermain signals. Each of these groups is discussed in sequence below.

Two nodes transmit main signals (S2 and S4): B7 TX transmits S2; andB38/40/41/XGP TX transmits S4.

Eight nodes receive high band diversity signals (S6, S8, S12, S14, S16,S18, and S24) as follows: node B41 a DRX receives S6; node B1/4 DRXreceives S8; node B40 receives S10; node B34 DRX receives S12; node B39DRX receives S14, node B3 DRX receives S16; node B2 DRX receives S18;node B7 DDRX receives S24;

Six nodes receive low band diversity signals (S26, S28, S30, S32, S34,and S36) as as follows: node B8/D28 a DRX receives S26; node B20 DRXreceives signal S28; node B26 DRX receives S30; node B13/B17 receivesS32; node B29 DRX receives S34; and node B28 b DRX receives S36.

Four nodes receive main band signals (S38, S40, S42, and S44): node B40a/B41 a RX receives S38; node B40 b RX receives S40; node B38/XGP/B41 bRX receives S42; and node B7/41 c RX receives S44.

Diversity filters CKT4 include filters F6, F8, F9, F11, F12, F14, F16,F18, F20, F22, F24, F25, F27, F28, F30, F32, F34, and F36.

Diversity switches CKT6 include high band switch SW2 and low band switchSW4 located on a thin SOI (silicon on insulator) die DIE2. High bandswitch SW2 may be a SP10T (single pole, ten throw) switch. Low bandswitch SW4 may be a SP7T (single pole, seven throw) switch.

High band switch SW2 receives high band diversity signal S46 at singlepole SP2, and transmits high band diversity signal S46 to a selected oneof ten throws (T6, T8, T9, T11, T13, T16, T18, T20, T22, and T24), to betransmitted towards diversity filters CKT4 as signals S6, S8, S9, S11,S13, S16, S18, S20, S22, and S24 respectively.

High band switch SW2 may include an additional throw (not shown) forgrounding.

Low band switch SW4 receives low band diversity signal S48 at singlepole SP4, and transmits low band diversity signal S48 to a selected oneof seven throws (T25, T27, T28, T30, T32, T34, and T36), to betransmitted towards diversity filters CKT4 as signals S25, S27, S28,S30, S32, S34, and S36 respectively.

Three filters (F6, F9, and F11) deserve special attention for futurereference. Filter F6 receives signal S6 from throw T6, and transmitsfiltered signal S6 to node B41 a DRX in transceiver CKT2.

Filter F9 receives signal S9 from throw T9 and transmits S10 (filteredsignal S9) to node B40 DRX. Filter F11 receives signal S11 and transmitssignal S10 (filtered signal S11) to node B40 DRX. If switch SW2 isthrown to T9, then node B40 DRX will receive signal S9 filtered throughfilter F9. Alternatively, if switch SW2 is thrown to T11, then node B40DRX will receive signal S11 filtered through filter F11. In thisfashion, diversity high band signal S46 is filtered by either filter F9(if T9 is thrown) or filter F11 (if T11 is thrown), and then transmittedas signal S10 to node B40 DRX. Of course, throws T9 and T11 may not bethrown (selected) simultaneously.

FIG. 3 illustrates a conventional high band pad CKT8, high band filtersCKT10, and high band switches CKT12 from FIG. 1.

In transmit mode for band 7, high band pad CKT8 receives signal S2 (band7 being transmitted from node B7 TX), passes this signal throughcapacitor CAP2 (to filter undesired very low frequency signals),amplifies this signal with amplifier PA2, and sends filtered amplifiedsignal S2 to duplexer DUPB7. Duplexer DUPB7 sends the amplified signaltowards main antenna ANTMAIN (not shown) as signal S52 in transmit mode.

Alternatively, in receive mode for band 7, duplexer DUPB7 receivessignal S52 from main antenna ANTMAIN, and sends this received signal asS50 towards a transceiver (not shown).

High band pad CKT8 also receives signal S4 (bands 38, 40 and 41 fromnode B38/40/41), passes this signal through capacitor CAP4 (to filterundesired very low frequency signals), amplifies this signal withamplifier PA4, and sends filtered amplified signal S4 to single pole SP6of switch SW6.

Switch SW6 is an SP4T (single pole, four throw) having one pole (SP6)and four throws (T54, T56, T58, and T60). If switch SW6 is thrown tothrow T54, then filtered amplified signal S4 (band B41 or band B38) issent to filter F54 in high band filters CKT10. Filter 54 sends filteredsignal S54 to high band switches CKT12, specifically to node TX B41 band to throw T54 in switch SW8.

Similarly, throw T56 sends signal S56 (bands B40 a and B41) to filtersF55 and F57. Filter 55 sends signal S55 (band 40 a) to high bandswitches CKT12. Filter 57 sends signal S57 (band 41 a).

Throw T48 sends signal S58 (band B41 c) to filter F58. Filter F58 sendsfiltered signal S58 to high band switches CKT12. Throw T60 sends signalS60 to filter F60. Filter F60 sends filtered signal S60 to high bandswitches CKT12.

High band filters CKT10 includes 9 filters: transmission filters (F54,F55, F57, F58, and F60), and reception filters (F37, F39, F63, and F65).In TDD operation, one of the transmission filters is being used, oralternatively one of the reception filters is being used. Filter F60 isa low pass filter, and the other filters shown in CKT10 are band passfilters.

High band switches CKT12 include two switches: SP6T (single pole, sixthrow) switch SW8 (including single pole SP8 and throws T62, T60, T54,T55, T57, and T58), and SP3T (single pole, triple throw) switch SW10(including single pole SP10 and throws T37, T39, and T64). Switch SW8and switch SW10 may be placed on a single die DIE4. Die DIE4 may beconstructed of MEMS (microelectromechanical systems) or may be solidstate SOI (silicon on insulator).

Briefly referring back to FIG. 2, diversity filters CKT4 include filtersF6 (band B41 a DRX), F9 (band B40 DRX), and FIG. 11 (also band 40 DRX).These filters filter a signal received from the diversity or MIMO(Multiple Input Multiple Output) antenna ANTDIV. These bands are alsoreceived through the main antenna ANTMAIN, and filtered by high bandfilters CKT10.

Switch SW8 is a transmission switch, and transmits signal TX RF1 to mainantenna ANTMAIN (not shown). For example, switch SW8 selects throw T55to transmit band B40 a TX through single pole SP8 towards main antennaANTMAIN (not shown) as signal TX RF1.

In contrast, switch SW10 is a reception switch, and receives signal RXRF1 at single pole SP10 from main antenna ANTMAIN (not shown). Forexample, switch SW10 selects throw T37, then receives RX RF1 at singlepole SP10 and transmits signal S37 (band B40 a RX) towards filter F37 indiversity switches CKT10 in route to transceiver CKT2.

TDD (Time-Division Duplex) alternately sends and then receives signalsin a given frequency band. In this fashion, band B40 a may bealternately sent, and then received over main antenna ANTMAIN (notshown) through switch selections as discussed above. Similarly, band B41a may be time-division duplexed using different switch settings.

Conventionally, as shown in FIGS. 2 and 3, different filters are usedfor receiving and for transmitting in each band. This conventionalapproach requires large numbers of filters. For example, high bandfilters CKT10 illustrates nine filters, and these nine filters areconventionally SAW (surface acoustic wave) or BAW (bulk acoustic wave)filters.

FIG. 4 illustrates a conventional single filter used for transmissionand reception of a single band. Specifically, filter F114 is used(alternately, under TDD (Time-Division Duplex) procedures) for filteringa band 38 signal for transmission, and then for filtering a receivedband 38 signal. Filter F114 is a “dual mode” filter because it filtersthe transmitted band 38 signal (in a first mode, see FIG. 5C) and alsofilters the received band 38 signal (in a second mode, see FIG. 5D).

Conventionally (in FIGS. 1, 2, and 3), different filters are used fortransmitting and for receiving because transmitted signals are highpower (typically 25 dBm, with high insertion loss filters), whereasreceived signals are low power (typically 0 dBm, with low insertion lossfilters). Thus, filters that are dedicated to received signals may usevery little power during filtering. In contrast, dual purpose filters(reception or transmission) must be relatively large, and will consumerelatively large amounts of power even when filtering received low powersignals.

However, there are some advantages to using a single dual purpose (ordual mode, or TX/RX) filter during LTE-TDD communications, such asreducing the number of filters, as shown in FIG. 4.

Filtering circuit CKT14 includes controller CONT4 controlled by controllines CL14, capacitor CAP6, amplifier PA6, switch SW14, switch SW12,filters (F114, F112, and F116), switch SW16, and capacitor CAP8.

Controller CONT4 may be controlled by control lines CL14 that mayinclude a bias voltage, a battery voltage, a clock signal, serial orparallel data signals, and enable signals.

From left to right, signal S100 includes a band 7 transmission signal ora band 38 transmission signal, is filtered by capacitor CAP6, amplifiedby amplifier PA6, received by single pole SP110 of switch SW14, thenswitched to throw T112 for the case of a band 7 transmission signal (orswitched to throw T114 for the case of a band 38 transmission signal).

FIGS. 5A-5D illustrate the use of a single filter (F114) fortransmitting and receiving in band 38 for LTE-TDD communications. FilterF114 is a “dual mode” filter because it filters the transmitted band 38signal (in a first mode, see FIG. 5C) and also filters the received band38 signal (in a second mode, see FIG. 5D).

FIG. 5A illustrates the switches and filtering of circuit CKT14 in FIG.4 for the case of transmitting band 7 (while omitting capacitors,amplifiers, and the controller for the sake of clarity). As discussedabove, switch SW14 throws the signal S100 to throw 112. This signalproceeds as signal S102 to filter F112, is filtered, then proceeds assignal S106 to throw T126 of switch SW16.

Signal S106 proceeds from throw T126 to single pole SP120, then exits assignal S110 towards main antennal ANTMAIN.

FIG. 5B illustrates the switches and filtering for the case of receivingband 7 (omitting capacitors, amplifiers, and the controller for the sakeof clarity).

A band 7 signal is received by the main antenna ANTMAIN as S110 (or B7RX), and is sent to single pole SP120 of switch SW16. Single pole SP120throws the signal to throw T126, and the signal exits as S106 towardsfilter F116. Filter F116 filters the signal and sends the filteredsignal as S114 (B7 RX) towards another location, such as towards atransceiver (not shown). Filter F116 may include a balun (not shown),and may output the received and filtered band 7 signal S114 asdifferential signals (a positive signal and a negative signal, notshown).

The position of switch SW14 is not shown in FIG. 5B. Power amplifier PA6may be turned off when receiving the band 7 signal, or switch SW14 maybe thrown to throw T114, or switch SW14 may be thrown to a ground (notshown). In other words, generally circuit CKT14 would not simultaneouslytransmit and receive in band 7, or else the high power transmission band7 signal would tend to interfere with the relatively low power receivedband 7 signal.

FIG. 5C illustrates the switches and filtering for the case oftransmitting band 38 (omitting capacitors, amplifiers, and thecontroller for the sake of clarity). Band 38 will be transmitted andreceived through the same filter F114 (transmitted in FIG. 5C, andreceived in FIG. 5D).

Switch SW14 throws signal S100 (B38 TX) from single pole SP110 to throwT114. Throw T114 send signal S104 to filter F114. Filter F114 sendsfiltered signal S108 to throw T124 of switch SW16, then to single poleSP120 of switch SW16. Single pole SP120 sends band 38 signal S110 tomain antenna ANTMAIN for transmission.

FIG. 5D illustrates receiving band 38 through filter F114 (previouslyused for transmitting in the same band 38 in FIG. 5C). FIG. 5D is basedon FIG. 4, but omits capacitors, amplifiers, and the controller for thesake of clarity). Thus, FIGS. 5C and 5D illustrate single filter F114being used for transmitting and receiving the same band 38 in TDD.

In FIG. 5D, a band 38 signal S110 is received by main antenna ANTMAINand sent to single pole SP120 of switch SW16. Switch SW16 throws thesignal to throw T124, then throw T124 sends signal S108 to filter F114.As discussed above, filter F114 now acts as a receiving filter in band38, instead of as a transmitting filter in band 38. Switch SW12 receivesfiltered signal S104 at throw T114, and throws this signal to singlepole SP120. Single pole SP120 sends received and filtered band 38 signalS112 upwards, possibly to a transceiver. Note that throw T114 of switchSW12 also serves as throw T114 of switch SW14.

Received and filtered band 38 signal S112 may be transformed by a balun(not shown) into differential signals (a positive signal and a negativesignal, not shown).

Thus, single filter F114 may alternately serve as a transmission filter(in FIG. 5C) and as a reception filter (in FIG. 5D) during time-divisionduplexing (TDD) in band 38.

FIG. 6 illustrates using single filters (to transmit and receive) formultiple LTE bands. In FIG. 6, filters F210 and F212 may each be usedfor filtering in a transmit mode (first mode) and then in a receive mode(second mode), similar to filter F114 discussed above in FIGS. 4, 5C,and 5D.

Specifically, circuit CKT16 includes amplifier circuit CKT18, SP2T(single pole, double throw) switches SW20 and SW22, and filters F210 andF212. Solid signal lines indicate the paths of transmission signals, anddashed lines indicate the paths of reception signals.

Starting at the top left, signal S210 is a transmission signal for bandsB38, B40, B41, and XGP. This signal is amplified by amplifier PA10 andsent as signal S212 to switch SW20. Switch SW20 throws this signal tofilter F210 as signal S214. Filter F210 transmits filtered signal S216towards an antenna (not shown. Filter F210 may also filter receptionsignals (dashed lines) in these bands.

Starting at the top right, filter F210 may receive a signal (dashedline, S218) from the antenna, and filter the signal and pass it toswitch SW20. Switch SW20 throws this filtered signal to the lower leftpole, and this signal passes to the left and down as signal S218. Thus,switch SW20 will be in a first position when transmitting, and in asecond position when receiving signals in bands B38 or B41 or XGP.

Similarly, switch SW22 and filter F212 may filter and transmit a signalin band B40, or may receive and filter a signal in band B40 (dependingupon the position of switch SW22.

When transmitting a band B40 signal S220, amplifier PA8 amplifies thesignal, filter F214 filters the signal and sends filtered signal S222 toswitch SW22, switch SW22 throws the signal to filter F212 as signalS224, then filter F212 filters the signal and sends signal S226 towardsan antenna (not shown, and not necessarily the same antenna that signalS216 was sent to).

Starting at the bottom right, filter F212 may receive and filter a band40 signal (dashed line S228)), then send the filtered signal to switchSW22. Switch SW22 throws this signal to the left and downward as S228.

The received signals S218 and S228 may be transformed into differentialsignals by baluns (not shown).

Thus, conventional communication circuitry requires too many filters.These numerous filters consume power and take up valuable space.

SUMMARY

A tunable filter reduces the total number of filters used in TDD(Time-Division Duplex) communication circuitry.

In a first embodiment, communication circuitry may include a tunablefilter and a first switch associated with the tunable filter. Thetunable filter may include a tuning component and a filtering component.The tuning component may be located with the first switch on a firstdie.

In a second embodiment, the filtering component may be located in alaminate underneath the first switch.

In a third embodiment, power amplifiers for amplifying transmissionsignals may be located on a second die, and the second die may belocated on the laminate.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 illustrates a conventional communication circuit with its majorcomponents.

FIG. 2 illustrates a conventional transceiver, diversity filters, anddiversity switches from FIG. 1.

FIG. 3 illustrates a conventional high band pad CKT8, high band filtersCKT10, and high band switches CKT12 from FIG. 1.

FIG. 4 illustrates a conventional single filter used for transmissionand reception of a single band.

FIGS. 5A-5D illustrate the use of a single filter (F114) fortransmitting and receiving in band 38 for LTE-TDD communications.

FIG. 6 illustrates using single filters (to transmit and receive) formultiple LTE bands.

FIG. 7 illustrates a power amplifier circuit associated with a dual modetunable filter (also known as a combined tunable filter), with a firstmode for transmitting and a second mode for receiving.

FIG. 8 illustrates a manufacturing embodiment of FIG. 7.

FIG. 9 illustrates some conventional bands of LTE-TDD (in MHz).

FIG. 10 illustrates a conventional overlapping bandwidth approach forreceiving signals in band B40 by overlapping two SAW (Surface AcousticWave) filters (SAW2 and SAW4) to filter the entire range of band B40.

FIG. 11 is similar to FIG. 10, but illustrates a dedicated filter F510for transmitting in band 41 c.

FIG. 12 illustrates using one tunable filter in combination with two SAWfilters to achieve split band coverage around the ISM band.

FIG. 13 illustrates using a tunable filter and two narrow edge SAWfilters to provide split band coverage around a central band.

FIG. 14 is similar to FIG. 13, except that filters SAW18 and SAW20 fromFIG. 13 have been replace by (or “merged into”) diplexer DIP2. In thisfashion, signal S410 replaces signals S404 and S406 from FIG. 13.

FIG. 15 is similar to FIG. 12, except that SAW20 (2496 to 2565) has beenreplaced by a band 7 range (2496 to 2570) of band 7 duplexer DUPB7.

FIG. 16 is similar to FIG. 13, except that band 41 a (2496 to 2565)filter SAW20 has been deleted.

FIG. 17 is similar to FIG. 12, except that the left portion of thetunable filter band (band 40 a (2300 to 2370)) has been replaced by anextended left portion of the tunable filter band (band 40 (2300 to2400)).

FIG. 18 illustrates circuitry implementing tuning component TUN8 of FIG.17, and illustrating a few additional features.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

FIG. 7 illustrates an amplifier circuit CKT20 including tunable filterand an associated switch. The tunable filter may include filteringcomponent F310 and tuning component TUN2.

Tuning component TUN2 may be a variable capacitor or an array ofcapacitors, and may be located with associated switch SW24 on single dieDIE8. The tuning component TUN2 and the associated switch SW24 may usethe same manufacturing technology, facilitating their placement on asingle die. For example (as shown in FIG. 8), they may be manufacturedby a single process such as SOI (Silicon-on-Insulator), or MEMS, or SiGewith high resistivity. This integration is not essential, but suchintegration will reduce size and cost.

The upper portion of amplifier circuit CKT20 is configured for band 7,and is identical to the top portion of high band pad CKT8 in FIG. 3. Intransmit mode for band 7, amplifier CKT20 receives signal S2 (band 7being transmitted from node B7 TX), passes this signal through capacitorCAP2 (to filter undesired very low frequency signals), amplifies thissignal with amplifier PA2, and sends filtered amplified signal S2 toduplexer DUPB7. Duplexer DUPB7 sends the amplified signal towards mainantenna ANTMAIN (not shown) as signal S52 in transmit mode.

Alternatively, in receive mode for band 7, duplexer DUPB7 receivessignal S52 from main antenna ANTMAIN, and sends this received signal asS50 towards a transceiver (not shown).

Die DIE8 includes tuning component TUN2 and switch SW24.

Starting at the lower left, capacitor CAP8 receives signal S320 (bandB38 or B40 or B41 for transmission), and sends signal S322 to amplifierPA12. Amplifier PA12 sends signal S324 to throw T304 of switch SW24.

In a transmitting configuration, switch SW24 throws signal 324 to singlepole SP300. Then single pole SP300 sends signal S326 to filter F310.Filter F310 (in a first mode, or transmission mode) transmits signalS328 towards an antenna (not shown).

Filter F310 is tunable, so that it may filter a band B38 signal, a bandB40 signal, band XGP signal, or band B41 signal, depending upon how itis tuned. Tuning component TUN2 is part of filter F310, and may belocated on a die holding switch SW24.

In a receiving configuration, received signals are indicated by dashedlines. Received signal S328 (starting at the lower right, and movingtowards the left) is received by tunable filter F310 (in a second mode),sent to single pole SP300 of switch SW24, thrown to throw T302, thensent downward as S330 towards a transceiver (not shown).

Thus, tunable filter F310 may operate in a first mode transmitting inband B38, or (after switching from throw T304 to throw T302) in a secondmode receiving band B38. After tuning to band B40, then tunable filterF310 may operate in a first mode transmitting in band B40, or (afterswitching from throw T304 to throw T302) a second mode receiving in bandB40. In this fashion, tunable filter F310 serves the role of at least 4different filters: transmit band B38, receive band 38, transmit bandB40, and receiver band B40. Further, if filter F310 tunably filters fortwo bands, then the associated single switch SW24 performs switchingfunctions for two bands (replacing switch SW20 and switch SW22 in FIG.6).

Coupled resonators (RES2 and RES4) act as a band pass filter, as shownin FIG. 8 discussed below. In one embodiment (not shown), fourresonators may be magnetically cross-coupled and may be symmetricallyspaced in a square pattern.

FIG. 8 illustrates a manufacturing embodiment of FIG. 7. In FIG. 8,circuit CKT22 is an embodiment of power amplifier circuit CKT20 of FIG.7, and includes laminate (or substrate) LAM2, power amplifier die DIE10(including amplifiers PA8 and PA10, not shown) on top of laminate LAM2,die DIE8 (including switch SW24 and tuning element TUN2, not shown) ontop of laminate LAM2, resonator RES2, resonator RES4 (magneticallycoupled to RES2), via VIA2, via VIA4, and bumps BUMP1 through BUMP4.Bumps BUMP1 through BUMP4 may be solder, or may be rectangular copperpillars (with low resistance), or other known attachment structures. Theresonators may be magnetically coupled, and may include additionalresonators.

Power amplifier die DIE10 may be GaAs or CMOS or SiGe. Die DIE8 mayinclude switch SW24 (not shown) for selecting between a first mode(transmitting or TX) and a second mode (receiving or RX), and mayinclude a tunable component TUN2 (not shown) of tuning filter F310 (notshown). Tunable component TUN2 may include a tunable array of capacitorsfor tuning filter F310. Tunable filter F310 may be a bandpass TDDfilter, may include RES2 and RES4, and may include tunable componentTUN2 located on die DIE8.

DIE8 and DIE10 may be a single package on a single laminate LAM2, asshown.

The manufacturing embodiment of FIG. 3 may be applied to any ASM(antenna switch module) where a single die includes band switching andtuning for LTE-TDD filters.

FIG. 9 illustrates some conventional bands of LTE-TDD (in MHz). Band B40ranges from 2300 to 2400 (large bandwidth of 100 MHz). Band ISM(Industrial, Scientific, and Medical, including WiFi) ranges from 2401to 2483 (bandwidth of 82 MHz). Band B41 ranges from 2496 to 2690 (verylarge bandwidth of 194 MHz, for U.S.). Broadly speaking, these threebands may be referred to as a low band, a central band (or exclusionband), and a high band respectively.

Together, bands B40 and B41 may be described as a “split-band” range,because the combined range is split into a low band (B40) and a highband (B41) by the central band ISM which must be avoided or excluded.

Band B41 encompasses bands XGP and B38. Band XGP (for Japan) ranges from2545 to 2575 (bandwidth of 30 MHz). Band B38 (for European Union) rangesfrom 2570 to 2620 (bandwidth of 50 MHz).

It is difficult to build filters simultaneously having large bandwidthsand having large attenuation at close offset frequencies (a “brick wall”at the end of the range of the filter). This difficulty also applies totunable filters.

Thus, it is difficult to build a single filter for receiving in band B40due to its large bandwidth (100 MHz) and its adjacency (at the high end,2400 MHz) to the low end of the ISM band (2401 MHz). Similarly, it isdifficult build a single filter for band B41 due to its very largebandwidth (194 MHz) and its adjacency (at the low end, 2496 MHz) to thehigh end of the ISM band (2483 MHz). Thus, multiple filters may be usedto cover band B40, as shown in FIG. 10.

FIG. 10 illustrates a conventional overlapping bandwidth approach forreceiving signals. This approach receives signals in band B40 (lowtarget band) and in band B41 (high target band). The ISM band (exclusionband) is intentionally excluded from (filtered out of) the receivedsignals.

SAW filters provide good edge characteristics. The upper edge (at 2400MHz) of SAW filter SAW4 coincides with the upper edge of band B40 (2400MHz). SAW4 passes signals at the upper edge of band B40 (the low targetband in this example), and excludes signals at the lower edge of theexclusion band. Alternatively, BAW (Bulk Acoustic Wave) filters alsoprovide good edge characteristics, and may be used in place of (or incombination with) SAW filters throughout this specification.

SAW6 similarly (or symmetrically) provides good edge characteristics,passing signals at the lower edge of band B41 (at 2496 MHz), andexcluding signals at the high edge of the exclusion band (2483 MHz).

Receiving (RX) in band B40 is performed by using two overlapping SAW(Surface Acoustic Wave) filters (SAW2 and SAW4) to filter the entirerange of band B40.

Specifically, band B40 is received by an overlapping combination of B40a (2300 to 2370 MHz, using filter SAW2) and band B40 b (2350 to 2400MHz, using filter SAW4). These two bands overlap by 20 MHz due to a 20MHz maximum modulation bandwidth for SAW filters.

Similarly, band B41 is received by overlapping combinations of band B41a (2496 to 2565 MHz, by SAW6), band B38 x (2545 to 2640 MHz, by SAW8),and band B7 (2620 to 2690 MHz, by filter F410). Band B38 x overlaps withband B41 a by 20 MHz, and overlaps with band B7 by 20 MHz, due to a 20MHz maximum modulation bandwidth for SAW filters.

Filter F410 may be a “reused” band 7 filter (not shown) from a duplexer(not shown), which is also being “reused” to filter the upper part ofband B41 (in addition to being used to filter band B7) In other words,this filter may be defined as filtering band B7 and band B41 c.

FIG. 11 illustrates a transmitting configuration similar to thereceiving configuration of FIG. 10, and illustrates a dedicated filterF510 for transmitting in band B41 c. SAW filters SAW10 and SAW12 overlapto receive all of band B40. Filters SAW14, SAW16, and F510 overlap totransmit all of band B41.

Similar to FIG. 10, SAW filters are used at the high edge of the lowtarget band and at the low edge of the high target band.

FIG. 12 illustrates using one tunable filter in combination with two SAWfilters to achieve split band coverage around the ISM band (the centralor exclusion band). As shown in FIGS. 9-11, the three bands of interestfor this embodiment are bands B40 (low target band), ISM (to beavoided), and B41 (high target band). As previously discussed, thesefilters may be used for receiving and for transmitting in TDD, withappropriate switching.

A tunable filter TUNFILT2 is configured to cover a low tunable band anda high tunable band. In FIG. 12, the low tunable band is labeled B40 a(2300 MHz to 2370 MHz, thus staying at least 20 MHz away from the loweredge of the exclusion band band).

SAW filter SAW4 (band B40 b) overlaps with the low tunable band (by 20MHz), and combines with the low tunable band to completely cover lowtarget band (B40, from 2300 to 2400 MHz).

As discussed in previous figures, a SAW filter (SAW4) is used to filterthe upper edge of the low target band, adjacent to the lower edge of theexclusion band.

Tunable filter TUNFILT2 is also configured to cover most of the upperpart of band B41 (2545 to 2690, or Bands B41 b, B41 c, XGP, and B38),thus staying at least 20 MHz away from the top of the exclusion band).See right portion of range of tuning component TUN4.

As discussed above, in order to fully cover band B40, SAW filter SAW4filters band B40 b (2350 to 2400). This range overlaps with band B40 aby at least 20 MHz, and also provides a good cutoff at 2400 MHz to avoidinterference with the lower edge of the ISM band (the central orexclusion band). Filter SAW18 may be described as a narrow edge filter,because it has a relatively narrow range and because it filters theupper edge of band B40.

Similarly, in order to fully cover band B41 (a high band), SAW filterSAW20 filters band B41 a (2496 to 2565). This range overlaps withTUNFILT2 by at least 29 MHz, and provides a good cutoff at 2496 in orderto avoid interference with the upper edge of the ISM band (the centralor exclusion band). Filter SAW20 may also be described as a narrow edgefilter.

FIG. 13 illustrates a switching configuration using a tunable filter andtwo narrow edge SAW filters to provide split band coverage around acentral or exclusion band. Specifically, amplifier circuit CKT24 is verysimilar to amplifier circuit CKT20 in FIG. 7, but is modified to providesplit band coverage.

The use of SPDT (single pole double throw) switches to facilitate asingle filter being used for transmitting and receiving in TDD wasdescribed in FIG. 5C and FIG. 5D respectively for band b38.

For the purpose of this specification, the term “SPDT” should beinterpreted broadly. For example, a SP3T (single pole triple throw)switch includes a SPDT switch, but merely has an additional throwavailable. In other words, adding an additional throw (or an additionalpole) for some other purpose does not prevent infringement.

Transmission signal S324 (including bands B38, B40, and B41) routes tothree switches: SW26, SW28, and SW30. These switches are shown on thepower amplifier side of the dual purpose filters, but may alternativelybe located on the antenna side of the dual purpose filters (not shown)with a slightly different configuration (not shown).

When transmitting in the tunable filter range (“split range”) of2300-2370 or 2545-2690, then switch SW26 receives signal S324 at throwTbTX and routes this signal to single pole SPA. Single pole SPA sendsthis signal to tunable filter TUN4. Tunable filter TUN4 filters signalS324 to pass band B40 a, or filters to pass bands B41 b and B41 c, orfilters to pass band B38, or filters to pass band XGP (depending uponhow tunable filter TUN4 is tuned). Tunable filter TUN4 passes a tunedsignal S402 towards main antenna ANTMAIN (not shown).

Tunable filter TUN4 may include a tunable component TUN6 that may belocated on a die with switch SW26, similar to the discussions above forFIGS. 7 and 8. Alternatively, component TUN6 may be a control portionthat controls tunable filter TUN4.

In the reverse direction, when receiving in the tunable filter range(“split range”) of 2300-2370 or 2545-2690, then tunable filter TUN4receives signal S402 from main antenna ANTMAIN (not shown). Tunablefilter TUN4 filters signal S324 to pass band B40 a, or filters to passbands B41 b and B41 c, or filters to pass band B38, or filters to passband XGP (depending upon the tuning of tunable filter TUN4).

Tunable filter TUN4 passes a filtered signal S408 to pole SPA of switchSW26. Pole SPA passes (not shown) the filtered signal S408 to throwTARX. Throw TARX sends filtered signal S408 to a transceiver (notshown). In FIG. 13, switch SW26 is shown in the transmission position,but may be switched to throw TARX for receiving in TDD.

For band B41 a, switch SW28 acts similarly to switch SW26. Filter SAW20filters transmission of signal S324 or reception of signal S404 in bandB41 a, depending upon the selection of switch SW28.

For band b40 b, switch SW30 acts similarly to switch SW28. Filter SAW18filters transmission of signal S324 or reception of signal S406 in bandB40 b, depending upon the selection of switch SW230.

FIG. 14 is similar to FIG. 13, except that filters SAW18 and SAW20 fromFIG. 13 have been replace by (or “merged into”) diplexer DIP2. In thisfashion, signal S410 replaces signals S404 and S406 from FIG. 13.

FIG. 15 is similar to FIG. 12, except that SAW20 (2496 to 2565) has beenreplaced by a band B7 range (2496 to 2570) of band B7 duplexer DUPB7.

FIG. 16 is similar to FIG. 13, except that band 41 a (2496 to 2565)filter SAW20 has been deleted. The filtering duties of SAW20 have beeneffectively shouldered by band 7 (2496 to 2570) duplexer DUPB7.

To summarize, FIG. 16 employs one tunable filter TUN4 and one SAW filterSAW18 to accomplish the filtering that previously required eight filtersin FIG. 3 (F54, F55, F57, F58, F37, F39, F63, and F65).

FIG. 17 is similar to FIG. 12, except that the left portion of thetunable filter band (band B40 a (2300 to 2370)) has been replaced by anextended left portion of the tunable filter band cover all of band B40(band B40 (2300 to 2400)). Also, SAW 18 has been deleted, since it is nolonger needed relative to FIG. 12. To document this change, the tuningcomponent has been named TUNFILT4 (instead of TUNFILT2 as in FIG. 15).This extension of the left portion of the tunable filter band eliminatesthe need for SAW18 of FIG. 12.

FIG. 18 illustrates filtering component F506 and tuning component TUN8of tunable filter TUNFILT4 of FIG. 17, and illustrates a few additionalfeatures. The bottom right portion of FIG. 18 is new, but the remainderof the figure is identical to FIG. 7. As discussed above regarding FIG.17, SAW18 has been eliminated.

Filter SAW20 and switch SW28 are retained from FIG. 13 to handle bandB41 a. All other frequencies within bands B40 and B41 (excluding bandB41 a) are filtered by filtering component F506 and tuning componentTUN8.

Switch SW32 is different from switch SW26 in FIG. 13. Switch SW32 is aSP3T switch, so that reception signals can be separated according towhether they are in the low portion of the tunable filter range (lowband of the split band coverage), or in the high portion of the tunablefilter range (high band of the split band coverage). If the receivedsignal is in the low portion (B40), then this is routed by switch SW32to RX2 as signal S504. If the received signal is in the high portion(B41 b, B41 c, B38, XGP), then this signal is routed by switch SW32 toRX1 as signal S502.

If the reception signal is in band B41 a, then this signal is filteredby SAW20, and routed by switch SW28 to RX1 as signal S502. Thus, thisreception signal in band B41 a is routed to RX1, the same as thereception signals in the high portion of the tunable filter range. Allrelatively high frequency reception signals are routed to RX1.

In contrast, band B40 is in the lower portion of the tunable filterrange, and reception signals in this range are routed to RX2 as signalS504.

Thus, FIG. 18 facilitates separate handling of received LTE TDD signalsby a transceiver. This separate handling by the transceiver facilitatesoptimized matching by the transceiver, because the low portion is verydifferent from the high portion (separated by almost 100 MHz).

A single die may include duplexer DUPB7, switch SW28, switch SW32,tunable component TUN8, and switch SW34. Filter component FILT506 may belocated outside of the single die. This single die may be SOI (siliconon insulator).

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. Communication circuitry comprising: a tunablefilter comprising a tuning component and a filtering component thatcollectively filter within a first band when tuned to the first band andfilter within a second band when tuned to the second band; a firstamplifier configured to amplify a first transmission signal; a firstswitch configured to: in a first mode, receive the amplified firsttransmission signal and pass the amplified first transmission signal tothe tunable filter; and in a second mode, receive a first receptionsignal from the tunable filter and pass the first reception signaltowards a transceiver; an LTE (Long Term Evolution) band 40 b filterthat is one of a SAW (Surface Acoustic Wave) filter and a BAW (BulkAcoustic Wave) filter; a second switch configured to: in the first mode,receive the first transmission signal and pass the first transmissionsignal to the LTE band 40 b filter; and in the second mode, receive asecond reception signal from the LTE band 40 b filter and pass thesecond reception signal towards the transceiver; a second amplifierconfigured to amplify an LTE (Long Term Evolution) band 7 transmissionsignal; and a duplexer configured to receive the amplified LTE band 7transmission signal; and wherein the tuning component and the firstswitch are located on a first die and the filtering component is notlocated on the first die.
 2. The communication circuitry of claim 1wherein: the first amplifier is configured to amplify the firsttransmission signal before the first transmission signal reaches thefirst switch; and the second amplifier is configured to amplify the LTEband 7 transmission signal before the LTE band 7 transmission signalreaches the duplexer.
 3. The communication circuitry of claim 1 furthercomprising a first SOI (Silicon On Insulator) die, wherein: at least aportion of the first switch, the second switch, and the tuning componentare located on the first SOI die; and the filtering component is notlocated on the first SOI die.
 4. The communication circuitry of claim 3further comprising a second SOI die that is distinct from the first SOIdie.
 5. The communication circuitry of claim 4 wherein the second SOIdie comprises the first amplifier, the duplexer, and the secondamplifier.